JDSLABS Objective2 + ODAC Combo Headphone amp By NwAvGuy model Frequency Response: +0.01, -0.01 dB (20Hz-20kHz) Output impedance:0.5 ohm Volume Potentiometer Taper: 15A or 3B Power:14-20V AC adapter with a standard 5.5 x 2.1 mm(not DC adapter). You can charge 9V battery from AC Jack and carry this amp. (battery not included) Size: 108.50 x 80.00 29.50 x mm Weight: 311g Accessories: cleat rubber/adapter